The effect of insect herbivory on the performance of Solanum campylacanthum on an African savanna
Insect herbivory can have important impacts on plant growth and fruit production. Plant growth can be stunted by the presence of herbivorous insects, while leaf performance also can be negatively affected. I conducted an insect exclusion experiment on the East African perennial woody shrub Solanum campylacanthum (Sodom apple) to examine the potential effect of insect herbivores on its performance. I selected 60 Solanum plants at the Mpala Research Centre in Kenya, and randomly assigned them to one of three enclosure treatments (Enclosure, Control, and Open). In the Enclosure treatment, the entire plant was enclosed using small mesh bridal veil; in the Control treatment, the plant was enclosed using veil with large holes cut in it; and in the Open treatment, the plant was handled but not enclosed. Prior to setting up the experiment, I measured the stem diameter, total branch length, crown dimension, height, number of leaves, and number of fruits of each plant. The veil enclosures were left on the plants for four months. At the end of the experiment, the veils were removed and the same measurements of the plants were taken again.
The exclusion of insects did not affect the growth rate of the Solanum plants. The mean change in plant height, branch length, stem diameter, and crown dimensions did not differ between the Enclosure and Control treatments. There was a trend of higher number of leaves on plants with insect exclusion in the Enclosure treatment. The exclusion of insects decreased the total number of fruits on the plants, but increased the proportion of fruits with insect damage. This was likely due to the exclusion of pollinators during the experiment. S. campylacanthum is native to the study area but considered a weed species. Herbivorous insects, however, do not appear to be an effective biological control agent in regulating its population.